The long term objective of this research is to explain how cell fates are specified and how developmental axes are established during vertebrate embryogenesis. The proposed experiments follow directly from our previous work and are relevant to studies on the establishment of developmental polarity in eggs and embryos, the transcriptional activation of the embryonic genome, the function of homeobox genes, and the development of antisense technology. There are 3 specific aims for the research: 1. To analyze how developmental polarity is established. The mechanism responsible for localizing maternal mRNAs to the animal and vegetal poles of frog eggs will be analyzed at the molecular and cellular level. Localized maternal mRNAs, such as Vgl which encodes a TGFbeta-like peptide growth factor, are likely play important roles in specifying cell fates during early embryogenesis. 2. Peptide growth factors are responsible for the induction of embryonic mesoderm in Xenopus. This is accomplished, in part, via the transcriptional regulation of homeobox genes. We propose to determine how peptide growth factors regulate the expression of homeobox genes. Activin and FGF are the peptide growth factors that will be used for these studies and their homeobox gene targets are Xhox3 and Mix2. In addition, we will further examine the function of the homeobox proteins in mesoderm induction and patterning. 3. We propose to develop an effective antisense approach to block gene expression in vivo as a means to test the function of cloned genes. Special attention will be given to chemically modified oligonucleotides as antisense agents.